Returns true if x and y are equivalent, false otherwise.
Returns false if x and y are equivalent, true otherwise.
Constructs a new Eq instance for type B where 2 elements are
equivalent iff eqv(f(x), f(y)).
A type class used to determine equality between 2 instances of the same type. Any 2 instances
xandyare equal ifeqv(x, y)istrue. Moreover,eqvshould form an equivalence relation.